1. Field of the Invention
The present invention relates to a seat ring and a butterfly valve fitting this seat ring thereto. More particularly, the present invention relates to a seat ring fitted to a butterfly valve in which a valve main body is divided into two sections composed of upper and lower sections in a horizontal direction of piping. The present invention also relates to the butterfly valve fitting this seat ring thereto.
2. Description of the Related Art
In general, piping of a butterfly valve is mainly of a so-called wafer type in which a pipe is supported by pipe flanges therebetween. There are also a screwing type, a clamping system, a housing type joint system, etc. in addition to the wafer type. The number of kinds of piping systems is gradually increasing.
Each of Japanese Utility Model Publication (KOKOKU) Nos. 3-32847, 3-54522 and 3-54523 shows a well-known butterfly valve constructed by a valve main body, a resilient seat ring, a valve body and an annular adapter. The valve main body is divided into two main bodies composed of upper and lower main bodies in a horizontal direction of piping. The resilient seat ring is fitted to this valve main body. The valve body is rotatably arranged within the seat ring and is pivotally supported and mounted to a valve rod extending through each of valve rod holes of the upper and lower main bodies and a valve rod hole of the seat ring. The annular adapter comes in contact with the seat ring.
In the above butterfly valve of the upper and lower dividing system, when the upper and lower main bodies each having a semicircular shape approach each other with the valve rod as a guide at an assembling time, an outer edge portion of the seat ring, a flange portion of the annular adapter and the upper and lower main bodies begin to firstly come in contact with each other in the vicinity of an X-axis of the upper and lower main bodies as a central line of a divisional circle. The outer edge portion of the seat ring is gradually compressed from a portion near the X-axis toward a direction of a Y-axis as a central line of the valve rod holes.
For example, synthetic rubber having an elastic property is used for the resilient seat ring. When one portion of this synthetic rubber is compressed, the shape of an incompressible portion is changed to relax stress caused by this compression.
When the upper and lower main bodies are in close proximity to each other in the butterfly valve of the upper and lower dividing system, the outer edge portion of the seat ring is not compressed at one time, but is gradually compressed. Therefore, the shape of an uncompressed portion is slightly changed to escape and direct compressing stress of a compressed portion to a region of the uncompressed portion. A deforming amount of this uncompressed portion is changed in accordance with frictional and slipping relations between inside faces of the upper and lower main bodies and an inside face of the outer edge portion of the seat ring.
Frictional force caused between the inside face of the outer edge portion of the seat ring and each of the inside faces of the upper and lower main bodies is applied to the butterfly valve in the horizontal direction at an angle approximately ranging from the Y-axis to 30 degrees in the upper and lower main bodies. This frictional force is applied to the butterfly valve in a more perpendicular direction at an angle approximately ranging from 60 degrees to the X-axis.
Namely, when the upper and lower main bodies are in close proximity to each other, an outside face of the outer edge portion of the seat ring entirely comes in contact with a groove portion of the flanged annular adapter in an angular portion equal to or smaller than an angle approximately ranging from the Y-axis to 30 degrees at which the seat ring and the upper and lower main bodies finally come in contact with each other. Therefore, a degree of freedom of deformation is limited in this angular portion so that no seat ring can be moved. Accordingly, the outer edge portion of the seat ring has no place to be escaped. Thus, this outer edge portion is wound inward by the frictional force caused in the horizontal direction between the inside face of the outer edge portion and each of the inside faces of the upper and lower main bodies.
The outer edge portion of the seat ring having a rectangular shape in cross section is compressed by the inside faces of the valve main body and an annular groove into which a side end portion of the seat ring arranged in the annular adapter is fitted. Accordingly, this outer edge portion has effects for preventing a fluid from being leaked from the butterfly valve.
However, to obtain these effects, a slight tapered portion must be formed on the outside face of a flange portion of the annular adapter and must be also formed in each of groove portions of the upper and lower main bodies surrounding this outside face. The annular adapter must be also moved in a Z-axis direction equal to a piping direction while the upper and lower main bodies approach each other in an axial direction of the valve rod. Further, when the upper and lower main bodies are completely coupled to each other, the entire outer edge portion of the seat ring must be compressed in a face-to-face direction equal to the Z-axis direction while a desirable compressing amount of the outer edge portion of the seat ring is secured. Accordingly, when the butterfly valve is assembled, pressing force for coupling the upper and lower main bodies to each other in a vertical direction must be increased to secure compressing force in this outer edge portion of the seat ring.
Further, it is necessary to increase a thickness of the outer edge portion of the seat ring by the compressing amount from a clearance definitely determined by a groove portion of the annular adapter and each of the inside faces of the upper and lower main bodies. Therefore, an outside diameter angular portion of the seat ring outer edge portion on its inner face side tends to be easily wound in by each of the inside faces of the upper and lower main bodies. Accordingly, there are many cases in which an assembly defect is caused and no desirable valve function can be obtained. In particular, in the case of a user requiring periodic cleaning of piping in food industries, etc., a plant or a dedicated jig or tool for disassembling and assembling the butterfly valve is insufficient. Therefore, winding-in of the seat ring is a factor of troubles when the butterfly valve is disassembled and reassembled.
One feature of the butterfly valve of the upper and lower dividing system is characterized in that the butterfly valve can be detached from piping by only disassembling the upper and lower main bodies of this butterfly valve without disassembling the piping itself. However, the outer edge portion of the seat ring is assembled with the compressing amount as mentioned above so that the upper and lower main bodies cannot be separated from each other by only detaching a bolt for fixing the upper and lower main bodies to each other. In this case, the upper and lower main bodies must be separated from each other by hammering an upper flange of the upper main body (as a flange for attaching a driving portion) with a hammer, etc. Otherwise, the upper and lower main bodies must be separated from each other by inserting a screw driver, etc. into a clearance between the annular adapter and one of the upper and lower main bodies and forcibly opening the butterfly valve. Accordingly, there is a fear of damaging the upper and lower main bodies and the annular adapter.
The flanged annular adapter and the upper and lower main bodies are not fixed to each other in a circumferential direction. Accordingly, when the driving portion heavy and voluminous in comparison with the butterfly valve is attached to the upper main body of the butterfly valve, there are often troubles that this driving portion is rotated together with the upper main body by vibrations of piping, etc. and is thereby inverted.
A valve seat formed in the seat ring is constructed by a spherical valve seat having the same diameter as an inside diameter of the seat ring. This valve seat is generally formed in a conical shape with respect to a piping direction. In a system using this seat ring, a pressure fluid is sealed by compressing the seat ring by means of the valve body and the upper and lower main bodies. Therefore, an escaping amount of the valve seat having the conical shape in the piping direction is large in comparison with the circumferential direction. Accordingly, measures for compensating an additional escaping amount of the valve seat must be taken with respect to a portion of this conical shape of the valve seat.